1. Field of the Invention
The present invention relates to a technology for positioning image carrier units in an image forming apparatus.
2. Description of the Related Art
Image forming apparatuses including copying machines such as electrophotographic copying machines, facsimile machines, printers, plotters, and multifunction products having the functions of two or more of these machines have been known.
In such an image forming apparatus, particularly in a multi-color image forming apparatus including a plurality of image carriers, it has been an important issue to accurately position a plurality of image carrier units (process cartridges) to be mounted on an image forming apparatus, so that images are prevented from being out of alignment including alignment of colors. The image carrier units each include an image carrier or the like that is a photosensitive member in a form of, for example, a drum (hereinafter, “photosensitive drum”) and also are configured to be attachable to and detachable from the image forming apparatus. Against this background, for example, Japanese Patent Application Laid-open Nos. H04-229889, 2004-177443, H10-7260, 2004-233902, 2001-242671, and 2001-222207 have proposed various methods for accurately positioning the image carrier units, and some of these methods are in practical use.
However, the above conventional techniques have problems in that the operability is low, for example, the operation to attach and detach a positioning member is complicated or difficult, and the cost is high.
In Japanese Patent Application No. 2005-332015 (Patent Application filed on Nov. 16, 2005), the applicant of the present application proposed a technique related to an image forming apparatus and the like that is able to solve the problems stated above.
However, it has become clear that the technique (first to third comparative examples explained later) disclosed in Japanese Patent Application No. 2005-332015 has some problems and need to be improved before practically utilized.
The problems will be explained with reference to FIGS. 8 to 11, 17, 30, and 31 in which the second comparative example, explained later, is shown. Referring to FIGS. 8 to 11, an image forming apparatus 7 includes process cartridges (image carrier units) 1Y, 1C, 1M, and 1BK. Each of the process cartridges 1Y, 1C, 1M, and 1BK includes a photosensitive drum as an image carrier, a charging device including a charging roller, a developing device including a developing roller, and a cleaning device including a cleaning blade. A bearing 17 rotatably supports a supporting shaft 16 for the photosensitive drum. A carrier supporting member 15 supports each photosensitive drum, and includes the supporting shaft 16 and the bearing 17. A positioning unit 70 that is configured to open and close is attachable to and detachable from the image forming apparatus 7, and positions each of the process cartridges 1Y, 1C, 1M, and 1BK via a corresponding one of the carrier supporting members 15.
As indicated by an arrow D in FIG. 8, when the positioning unit 70 is set to the image forming apparatus 7, positioning holes 35a and 35b on the left and right sides of a positioning holding member 32A are fitted with positioning pins 36a and 36b on the left and right sides of the image forming apparatus 7 and are arranged at positions opposite to the positioning holes 35a and 35b. 
The positioning unit 70 includes the positioning holding member 32A having sets of planes 78 and 79 as holding portions, four pressing members 44A in correspondence with the carrier supporting members 15 for the process cartridges 1Y, 1C, 1M, and 1BK each of which is configured to move between a non-pressing position and a pressing position, springs 71 that serve as biasing units each of which biases the corresponding one of the pressing members 44A in such a direction that the pressing member 44A moves toward the pressing position, and a sliding member 41A that movably supports the pressing members 44A and serves as a movable member being slidably and movably supported by the positioning holding member 32A between a first position shown in FIG. 10 that corresponds to the non-pressing position and a second position shown in FIG. 11 that corresponds to the pressing position. Each set of the of planes 78 and 79 is provided in four openings as attachment holes 77 in which the carrier supporting members 15 are respectively held by the weight of the process cartridges 1Y, 1C, 1M, and 1BK when the positioning unit 70 is closed on the image forming apparatus 7 after being swung in the direction indicated by the arrow D. The non-pressing position shown in FIG. 10 is a position at which each pressing member 44A is not in contact with the corresponding one of the carrier supporting members 15 placed on the planes 78 and 79 of the attachment hole 77. The pressing position shown in FIG. 11 is a position at which each pressing member 44A is pressing and positioning the corresponding one of the carrier supporting members 15 that are placed on the planes 78 and 79 of the attachment hole 77.
As shown in FIGS. 8 to 11, when any of the photosensitive drums or the like needs to be replaced, i.e., when any of the process cartridges 1Y, 1C, 1M, and 1BK or the like needs to be replaced, the sliding member 41A that is slidably supported by the positioning holding member 32A is slid to the first position as shown in FIG. 10, toward the left side of the drawing. As a result, the pressing members 44A are placed in the non-pressing positions at which the pressing members 44A are positioned away from the bearings 17 of the photosensitive drums. Subsequently, the positioning unit 70 is swung in the direction indicated by an arrow C in FIG. 8, centering on hinge pins 34, so that the positioning unit 70 is opened from the image forming apparatus 7 and is placed in an open position.
When the replacement of the photosensitive drum or the like is finished, the positioning unit 70 is swung in the direction indicated by the arrow D in FIG. 8, centering on the hinge pins 34, so that the positioning unit 70 is attached to and set to the image forming apparatus 7. Subsequently, the sliding member 41A is slid as shown in FIG. 11, toward the right side of the drawing, to be in a set state in the second position. As a result, the pressing members 44A are placed in the pressing positions at which each of the pressing members 44A is in contact with and pressing the corresponding one of the bearings 17 of the photosensitive drums. Thus, the bearings of the photosensitive drums are positioned and held in their respective predetermined positions.
As shown in FIG. 17, on the sliding member 41A is a pin 93 used for moving the sliding member 41A. The positioning holding member 32A has a cover 90. Provided on the cover 90 is an operation lever 94 that is made of a resin and has a guiding groove 94b, which is configured to be fitted with the pin 93 on the sliding member 41A.
FIG. 30 is a view of the operation lever 94 from the back. The sliding movement of the sliding member 41A caused by an operation of the operation lever 94 will be explained with reference to FIG. 30.
The operation lever 94 has the guiding groove 94b, a rotation shaft 94a that is a basal portion of the operation lever 94, and a handle unit 94c that is a portion actually used in manual operations. When the operation lever 94 is turned by a predetermined angle in the direction indicated by an arrow K, centering on the rotation shaft 94a, i.e., when the operation lever 94 is swung, the pin 93 on the sliding member 41A is moved in the guiding groove 94b in a substantially horizontal direction. Thus, the sliding member 41A is slid in the same direction.
However, a first problem arises that a user or an operator (hereinafter, “operator”) who is not familiar with the operation of the apparatus is not able to identify a position at which it is possible to improve the operability and the workability of the operation lever 94.
In addition, especially for a full-color image forming apparatus or the like, the positioning holding member 32A tends to be manufactured so that the length thereof extends in the left-and-right direction (the horizontal direction). In such a case, to improve the level of precision in positioning of the positioning holding member 32A with respect to the image forming apparatus 7, it is necessary to arrange the positioning holes 35a and 35b and the positioning pins 36a and 36b so that they have as large a distance as possible therebetween in the left-and-right direction (in the horizontal direction) of the positioning holding member 32A. In consideration of reduction in the weight and the cost of the positioning unit 70, it is generally common to manufacture the positioning holding member 32A with sheet metal or the like and the cover 90 with a resin or the like. Thus, the positioning unit 70 and the cover 90 tend to slightly warp on either end thereof in the left-and-right direction (in the horizontal direction). As a result, the positioning holes 35a and 35b and the positioning pins 36a and 36b do not fit with one another all the way. Thus, a second problem arises that it is difficult to activate a locking device (not shown).
Further, when the operation lever 94 is swung in the direction of the arrow K so that the sliding member 41A makes the sliding movement to one of the first position and the second position, an operator who is not familiar with the operation of the apparatus may apply a force in the direction indicated by an arrow E directing from the cover 90 toward the operator. Thus, a third problem arises that the applied force may damage or break the operation lever 94 that is made of, for example, a resin.
Furthermore, when the operation lever 94 is operated incorrectly by an operator who is not familiar with the operation of the apparatus or an unspecified person, a fourth problem arises that the positioning of the process cartridges (the image carrier units) 1Y, 1C, 1M, and 1BK by the positioning unit 70 is cancelled suddenly or unexpectedly or becomes insufficient.